The FDA has some frequently asked questions about azodicarbonamide. Here is a summary: It was used as a dough conditioner or a whitening agent. It breaks down to a many chemicals, one of which is called semicarbazide which caused tumors if eaten by female mice but not males. The FDA contends that it is still safe product because this is only at extremely high levels well above human consumption.
Azodicarbonamide is in over 500 products but became a well known ingredient when found in Subway bread, but the Environmental Working Group found it in over 500 products. Though it was removed from the Subway sandwiches since 2014. The products are well known commercial products like Wonderbread, Little Debbie and Pilsbury Dinner Rolls.